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Wash recycling – at the most optimum

 

A sand washing plant, predominantly designed by an OEM for sand processing applications, has been successfully installed in a recycled aggregates operation. The plant has proven that it can cope with construction and civil engineering wastes and transform them into clean, consistent recycled products.

Construction and demolition waste management specialists R Collard Ltd, based in Eversley, Hampshire, United Kingdom, has opened a state of the art aggregate washing plant. 

Terex Washing Systems (TWS) designed and supplied the washing plant, based at R Collard’s recycling facility. It incorporates the latest technology to enhance the quality and efficiency of the facility’s recycling process.  The installation was specified and project managed by Duo Plc, the TWS distributor in England and Wales.

Capable of throughputs up to 120 tonnes per hour (tph), with annual production capacity of about 250,000 tonnes, the system provides a local source of high grade recycled aggregate products 12 months of the year to enhance the efficiency and environmental performance of regional construction and civil engineering developments in the south of England. 

“Transport is a major factor in the cost of aggregate so our investment in this plant is a direct response to increasing demand for high quality, affordable recycled product in our catchment area throughout south east England,” Collard’s founder and managing director Robert Collard explained. “The refinements to the technology involved will enable us to process more wastes than we collect from local sites and create a truly closed loop recycling system for construction waste in the south of England.”

TWS’s recycling processes can transform construction and civil engineering wastes into clean, homogenous recycled products. They remove lightweight and deleterious contaminants and extract silt and clay which can bind otherwise commercially viable aggregates together. Material processed at the site will be used in a broad range of construction projects. 

The plant boasts a number of innovative new features including:

  • Hydrocyclone technology producing high grade coarse sand product with less than two per cent silt content.
  • Integrated sorting systems removing non-mineral contaminants, to a greater extent than conventional dry systems. More wastes can subsequently be used as feedstock.
  • All year round operation due to a new feeder system that processes cohesive material, even when its moisture content changes.
  • Fully adjustable, modular components that enable the generation of bespoke products.

The wash plant set-up at R Collard  is an innovative, effective and coherent approach for the recycled aggregates industry. It constitutes scalping (a Warrior 1400), aggregate rinsing and sand washing (an AggreSand 165 triple-deck screen), aggregate scrubbing and sizing (an AggreScrub 150) and water treatment and recycling (thickener and filterpress). 

The process starts with an AggreScalp heavy-duty scalping unit, particularly suited to claggy and clay contaminated/high soil content feeds. This unit removes excess oversize before passing the bulk of material to the subsequent washing equipment.  The AggreScalp includes a magnet to capture ferrous metals, specifically located to allow such metals to be extracted in freefall before transfer to the AggreSand.

The AggreSand incorporates a 5m x 1.5m (16’ x 5’) triple-deck screen producing a clean 50mm+ oversize for subsequent crushing and delivering the mid- and bottom-deck outputs to its partnering AggreScrub 150 for subsequent attrition and sizing. The feed material contains high root content which is effectively removed by the AggreScrub. The flotation capabilities of the AggreScrub are ideal for addressing the variable contaminants found in recycled aggregate sources such as paper, wood and light plastics. These contaminants, together with most of the water and liberated sand particles, are passed from the rear of the AggreScrub to the integrated trash screen. This step recovers the lightweight contaminants as a waste and allows the water and sand to be collected. 

The claggy and clay contaminated/high soil feeds on the conveyor.
The AggreSand 165 produces a clean 50mm+ oversize for subsequent crushing, attrition and sizing.

In addition to flotation, the AggreScrub’s other key purpose is heavy attrition to liberate adherent clays, producing clean organic-free aggregates for a wide range of construction requirements.  A 3.6m x 1.5m (12’ x 5’) part-rinser integrated within the AggreScrub modular chassis provides the final product splits requested by Collard.

Underflows from the trash screen and the aggregate sizing screen are collected and pumped back to the AggreSand to recover any saleable fine material and ensure maximum efficiency of water management. 

The 120 tph sand plant integrated within the AggreSand produces two high quality sands from the recycled feed material, suitable for concrete, pipe bedding and general construction requirements. Sand and water from the AggreSand screen, together with return water and fines from the AggreScrub, is recovered via the integrated hydrocyclones, producing coarse and fine sand fractions. These are dewatered by the system to ~12 per cent moisture content, providing clean and ready to handle material stockpiles.

All dirty water gravity flows from the AggreSand’s cyclones to the congruent water management system. This phase includes an 8m rake thickener with polyelectrolyte (flocculant) dosing, controlled on a batch basis with automated monitoring.  Suspended solids coagulate and sink to the bottom of the thickener and are drawn to the central outlet by the constantly rotating rakes. This thickened mud is pumped to a large homogenising sludge buffer tank while clean, recycled water overflows from the thickener to a storage tank. A high frequency screen featuring a fine steel mesh is installed between the thickener and the water tank, removing any residual organics and floatable contaminants such as polystyrene balls.

Sludge from the homogenising buffer tank is delivered to the 150 plate (2m x1.5m) filter press via a powerful double centrifugal pump, delivering sludge to the press at up to 16 bar (or 232 psi) pressure.  This effectively reduces waste output to a highly compressed, low moisture content by-product that can be easily handled and removed from the site.

This thickener and filter press combination recycles 90 per cent of the water used in the plant. In turn, it allows the complete system to operate with only 30m3 of water per hour, provided by the 63.5mm (or 2.5”) mains supply.

The TWS washing plant brings an advanced, effective and efficient approach to the recycled aggregates industry, incorporating the very latest technology to enhance the quality and efficiency of the recycling process while significantly reducing the cost, fuel consumption and carbon footprint of supplying recycled aggregates. •

For more information about this particular washing system and the full product offering, visit
terex.com/washing

In Australia, the distributor of the Terex Washing Systems product is Terex Jaques. Visit:
terex.com/mps/en-au

 

This article appears in the August edition of Quarry Magazine

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